1. Field of the Invention
The present invention relates to a semiconductor laser which emits a light beam having a wavelength in a green-blue region.
2. Description of the Related Art
Recently, in order to increase the density of an optical disc and enhance the resolution of a laser printer, a semiconductor laser having a short wavelength has been expected. As a semiconductor light-emitting element which emits a light beam having a short wavelength, such as a blue or green light beam, a semiconductor laser using a ZnSe type II-VI compound semiconductor has been widely studied and developed.
For example, a gain waveguide type semiconductor laser as shown in FIG. 9 is reported in Electronics Letters, 31 Mar. 1994, Vol. 30, pp.568 to 569.
A semiconductor laser 100 shown in FIG. 9 includes: a multi-quantum well layer 105 made of ZnCdSe; a pair of light confinement layers 104 and 106 respectively made of p-type ZnSSe and n-type ZnSSe, sandwiching the multi-quantum well layer 105 therebetween; and a pair of cladding layers 103 and 107 respectively made of p-type ZnMgSSe and n-type ZnMgSSe, sandwiching the light confinement layers 104 and 106 therebetween. The above structure is formed on a buffer layer 102 made of ZnSSe which is formed on a GaAs substrate 101. On the cladding layer 107, a p-type ZnSSe layer 108, a p-type ZnSe layer 109, a multi-quantum well layer 110 made of p-type ZnSe and p-type ZnTe, and a contact layer 111 made of p-type ZnTe are deposited in this order. The p-type ZnSe layer 109, the multi-quantum well layer 110 and the contact layer 111 are etched into a striped shape to form a striped structure 115. Both sides of the striped structure 115 are buried by insulating layers 112. Electrodes 113 and 114 are formed on the bottom face of the GaAs substrate 101 and the upper surface of the contact layer 111, respectively.
In the semiconductor laser 100, a current flowing into the multi-quantum well layer 105 is allowed to be distributed by the striped structure 115 so as to form carrier distribution in the multi-quantum well layer 105, thereby controlling a lateral mode.
Moreover, Electronics Letters, 9 Dec. 1993, Vol. 29, pp.2192 to 2193 has reported that a ridge refractive index type semiconductor laser having both sides of a ridge buried by insulating films, continuously oscillates at room temperature. Furthermore, Appl. Phys. Lett. 63(17), 25 Oct. 1993, pp. 2315 to 2317 has reported that a ridge refractive index type semiconductor laser using polycrystalline ZnS as a burying layer, oscillates in pulse at room temperature.
In a semiconductor laser, it is important to appropriately control a lateral mode of an oscillating laser light beam for realizing stable oscillation in a single mode. Although a lateral mode is controlled by using a gain waveguide mechanism or a refractive index waveguide mechanism in a conventional semiconductor laser described above, continuous oscillation of a stable single mode has not been realized yet. The reason for this is as follows. Since the combinations in group II-V compound semiconductors, with which a semiconductor layer having good crystal quality can be formed, are limited in the current techniques, it is difficult to manufacture a stripe-shaped semiconductor structure whose sides are buried by using a suitable material so as to realize a gain waveguide mechanism or a refractive index waveguide mechanism.
Although a burying layer made of silicon oxide, aluminum oxide, polycrystalline ZnS or the like is used in the above conventional examples, these materials are not generally preferred as materials for a semiconductor laser.
The reasons for this are as follows. Since these burying layers have a large heat resistance, these burying layers cannot sufficiently conduct the heat generated in the active layer. Therefore, the semiconductor laser is deteriorated over time, resulting in a decrease in reliability of the semiconductor laser. Moreover, since it is generally difficult to deposit a thin film made of these materials on order of several .mu.m, it is difficult to bury a large step difference. Thus, it is difficult to flatten the upper surface of the semiconductor laser. Accordingly, it is also difficult to mount the semiconductor laser facedown.